Terry.Li-彬

用 Maven 做项目管理在 Java世界中我们很多的开发人员选择用 Ant来构建项目，一个 build.xml能够完成编译、测试、打包、部署等很多任务，但我们也碰到了很多的问题，如 jar文件管理混乱，各个项目结构和 build.xml相差很大等等。而 Maven的出现，给项目提供了更多的支持。



1        简介 Maven 作为 Apache 的一个开源项目，旨在给项目管理提供更多的支持，主页地址为 http://maven.apache.org 。它最早的意图只是为了给 apache 组织的几个项目提供统一的开发、测试、打包和部署，能让开发者在多个项目中方便的切换。很多伟大的事业，出发点都很简单， ebay 就是很好的例证。而 maven 的成功又一次验证了这一点，越来越多的项目开始使用 maven 。
基本原理
Maven 的基本原理很简单，采用远程仓库和本地仓库以及一个类似 build.xml 的 pom.xml ，将 pom.xml 中定义的 jar 文件从远程仓库下载到本地仓库，各个应用使用同一个本地仓库的 jar ，同一个版本的 jar 只需下载一次，而且避免每个应用都去拷贝 jar 。如图 1 。同时它采用了现在流行的插件体系架构，只保留最小的核心，其余功能都通过插件的形式提供，所以 maven 下载很小（ 1.1M ），在执行 maven 任务时，才会自动下载需要的插件。
这个基本原理与 Pear ――ＰＨＰ扩展与应用库（ the PHP Extension and Application Repository ）的原理非常相似，都有一个官方的仓库，都是微内核，通过网络将需要的文件下载到本地，通过官方仓库将相应的类库进行统一管理。 Pear 已经成为 PHP 开发事实上的标准，而 Maven 在 Java 世界的地位也逐渐加强，成为标准指日可待。
另外由于插件的易开发性，现在有了非常多的可供选择的插件，如与 eclipse 结合的插件，与 test 相关的插件，后面我们结合 maven 在项目中的使用进行详细介绍。

2        项目管理 Maven 官方把 maven 定义为一个项目管理工具，我们不妨看看 maven 能给我们的项目提供哪些好的支持。
2.1       项目标准化 Maven 一个重要特性是定义了项目的标准模板，官方说法是最佳实践。可以通过命令： mvn archetype:create -DgroupId=com.mycompany.app -DartifactId=my-app 创建一个单一的 maven 项目。创建好的项目，具有了特定的项目结构。这个项目结构是参考业界的最佳实践而成，为后面使用统一的 maven 命令打下了基础，如测试 mvn test 、打包 mvn package 等，无需写一行脚本，就可以方便的实现众多功能。 Maven 还提供其它一些类型模板，可以通过添加 -DarchetypeArtifactId= ｛ type ｝创建，如 -DarchetypeArtifactId=maven-archetype-site ，生成 site 类型的项目。
同时一些好的开源软件使用了 maven ，也能作为很好的项目模板，如 Equinox （ Appfuse 的简化版），它的 pom 定义了对 hiberante,spring… 的依赖，可以通过 ant new -Dapp.name=NAME 快速生成项目原型，然后对 pom 文件进行裁减，以符合自身项目的需要。
有了这个标准，项目间能方便的进行交流，你也很容易了解其它使用 maven 项目的结构。对于企业来说，引入 maven 就自然引入了规范，这可比费时费力的写文档，定规范有效的多了。
2.2       文档和报告 使用 mvn site 可以快速生成项目站点， apache 很多开源项目站点都采用 maven 生成，会出现 built by maven 字样的图标。
而 maven 提供的针对如 junit ， checkstyle ， pmd 等的插件，能够方便的进行测试和检查并能直接生成报告。使用都很简单，如 mvn surefire-report:report 就能自动进行 junit 测试，并生成 junit 报告， mvn pmd:pmd 生成 pmd 报告。具体使用可以在 http://maven.apache.org/plugins/index.html 找到。
2.3       类库管理 Maven 一个很重要的特色就是类库管理。通过在 pom.xml 中定义 jar 包版本和依赖，能够方便的管理 jar 文件。以下是一个简单的 jar 定义片断：

<dependency>                                                                              <groupId>org.hibernate</groupId>       <artifactId>hibernate</artifactId>       <version>3.1</version>       <type>jar</type>       <scope>runtime</scope>   </dependency>

这个片断告诉我们，依赖的 jar 包 groupId 为 org.hibernate ， artifactId 为 hibernate ，版本为 3.1 ， scope 为 runtime 。在实际项目中，会将 M2_REPO(maven 本地仓库地址 )/ org/hibernate / hibernate /3.1/ hibernate -3.1.jar 放入 classpath 。
同时 maven 会通过 pom.xml 管理 jar 包间的依赖。比如上面的 hibernate-3.1.jar 同级目录肯定会有一个 hibernate -3.1.pom ，在这个 pom 文件中指定了这个 jar 对其它一些 jar 的依赖。而这个 pom 文件是远程仓库提供，无需进行修改，执行 maven 相关命令就会自动根据相关依赖去下载 jar 包。这样只需定义对 hibernate 的依赖而无需关心相关 jar ，在构建项目上方便了很多。
因为 pom 文件对 jar 的管理，也产生了一个很吸引人的特性：项目文件很小。以往一个 web 项目中， jar 文件都要放入 WEB-INF/lib 下，并放入 cvs(svn) 中，很容易就达到几十 M 。而通过 maven ，只需一个 pom.xml ，在执行 mvn eclipse:eclipse 时再去远程仓库下载，项目文件一般只需几百 K 。
2.4       发布管理 使用 maven 可以方便的进行项目发表管理。在项目开发到一定阶段，可以使用 mvn package 打包，它会自动先运行 mvn test ，跑所有的 testcase ，只有全部通过才能正确打包。生成的 war 包（如果项目的 packaging 为 war ）在 target 目录下。这个 war 包与使用 ant 脚本生成一样，但无需一行脚本，这也是 maven 对比 ant 的优势之一。使用 mvn install 将编译和打包好的文件发布到 distributionManager 指定的远程 repository 。使用 mvn deploy 可以自动管理项目版本。
  
3         使用 maven Maven 使用简单，插件丰富且经过大量项目考验，在项目中引入的风险很小。笔者在项目中使用 maven ，新进员工在半小时内就能成功使用 maven 构建项目，并很快掌握几个常用的命令。 Maven 也不需要什么特殊的设施。如果项目全部使用开源软件，并且不需要 maven 管理项目版本，只需要一个 SCM 环境（ CVS 或 SVN ），共享开发源码就可以。把 pom.xml 中的 repository 设为官方地址就行，配置如下：

<repository>       <id>central</id>       <url>http://www.ibiblio.org/maven2</url> </repository>

这个官方 remote repository 上有非常多的开源软件，应该能满足大部分项目的需要。如果有项目需要而它上面暂时还没有的软件，或者希望使用公司内部的软件，那么就需要自己配置一个 repository 了。
3.1       自建私服 传奇私服大家应该都听过，一个网吧自己搞个私服，一伙人免费在上面砍杀。官方因此少赚了很多钱，因此总想打击。而 maven 官方却对自建私服很是支持，我们总算可以正正当当搞把私服了（ Springside 的老大江南白衣就是创建私服的好手）。我们就来介绍下自建私服的最快方法。
首先需要一个 http server ，找台服务器装上 apache 就行。放一个空的 maven 目录到 htdocs 下，假设服务器 ip 为 192.168.0.1 ，确认能用 http://192.168.0.1/maven 访问到。然后在自己机器上装好 maven2 ，初始化好项目，在 pom.xml 放入需要的 jar 定义，运行如 mvn eclipse:eclipse 就自动从官方下载 jar 到本地，如果不做配置，默认本地 repository 为 ${user.home}/.m2/ 。对于 windows xp 来说一般在 C:\Documents and Settings\ ％ username%\.m2 下，其中％ username ％为操作系统登录用户名。这时你可以看到 ${user.home}/.m2/ 下多了个 repository 目录，里面有很多的项目相关 jar ，目录按 groupId/ artifactId/version 排好。把 repository 目录整个拷贝到 apache 服务器的 maven 目录下，如果需要官方缺少的 jar 或公司内部 jar ，仿照这个目录结构，做好 jar 放到 maven 目录下。自建私服成功！
要使用私服，只需修改 pom.xml ，在 repository 配置后加上：

<repository>       <id>companyName</id>       <url>http:// ${ip}/maven</url> </repository>

这样需要下载 jar 时，会先到本地 repository 查看，没有下载过再到官方搜索，没有找到再到后面的 repository 查找。
3.2       安装配置 Maven 的安装很简单：
1.         从 apache 网站上下载 maven 安装包，实际上就是个压缩文件。将其解压到你想要存放 maven 的目录中。在这里假设你将 maven 解压到 C:\Program Files\Apache Software Foundation\maven-2.0.4 中。
2.       将 C:\Program Files\Apache Software Foundation\maven-2.0.4\bin 设到你的系统环境变量%PATH%中。
3.       同时确保你已经将你的JDK安装目录设为java_home系统变量。
4.         打开个命令行窗口，运行 mvn –version 验证是否安装成功。
5.         如果使用 eclipse ，在运行 mvn eclipse:eclipse 生成 eclipse 项目文件后，需加入 M2_REPO 到 Classpath Variables 中，指向 本地 repository ，例如： C:/Documents and Settings/Owner/.m2/repository 。
3.3       基本使用流程 在项目进程中，不必做什么配置，在 pom.xml 同级目录， cmd 使用简单的 maven 命令，就可以完成初始化 -> 开发 -> 测试 -> 发布 的全过程。 Maven 的基本使用流程如下图：

其中在初次使用命令 mvn eclipse:eclipse 时会下载很多的插件和 jar ，可能需要较长的时间，建议泡杯咖啡，和同事吹吹牛。如果失败，可能是网络问题，可以重新运行 mvn eclipse:eclipse ，已下载好的插件和 jar 不会再下。运行 mvn test 和 mvn package 等命令，产出物都会放在 target 目录下。如果在使用过程中有什么问题，也可以和我联系， mail:pesome@gmail.com ，我们一起来尝试解决。
  
总结：
Maven 作为新的项目管理工具，简单易用，能对项目的各个阶段提供大力支持，同时由于它易扩展的插件体系架构，出现了越来越多的插件，也使得其功能更加强大。短短一篇文章，实在很难把其特点一一尽述， maven 还有很多好用的功能和插件等待我们去使用和开发。而学习新技术的最好方式就是实践，大家如果有兴趣，尽快下载一个最新版，开始你的 maven 之旅吧！
  
作者简介：张俊，网名 pesome ，上海交大软件工程硕士， 2 年 JavaEE 开发经验，资历尚浅。去年下半年开始接触 spring 等开源软件，并产生了浓厚的兴趣。今年 3 月开始做 www.openfans.net ，用一堆开源软件搭建而成，希望为中国的开源事业做出一点贡献。
  
参考文档：
1.       http://maven.apache.org 官方网站文档
2.       http://www-128.ibm.com/developerworks/cn/opensource/os-maven2/ Maven2 的新特性


Posted by kevinwu on December 15, 2006 09:22 PM | 全文 |MAVEN|del.icio.us|VIVI|365key|blogChina|Poco|SOHU|Hexun

相关文档＿
使用Maven构造Turbine项目 - Dec 15, 2006
Maven 让事情变得简单 - Dec 15, 2006
在 Eclipse 中利用 Maven - Dec 15, 2006
maven2.0学习笔记（转载） - Dec 15, 2006
Maven入门--概念与实例（转载） - Dec 15, 2006

Maven入门--较复杂的实例

</encoding>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-jar-plugin</artifactId>
                <configuration>
                    <archive>
                        <addMavenDescriptor>false</addMavenDescriptor>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-war-plugin</artifactId>
                <configuration>
                    <archive>
                        <addMavenDescriptor>false</addMavenDescriptor>
                    </archive>
                </configuration>
            </plugin>

            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-javadoc-plugin</artifactId>
                <configuration>
                    <charset>UTF16</charset>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">

Maven入门--概念与实例

3 标准目录布局
    Maven为工程中的源文件，资源文件，配置文件，生成的输出和文档都制定了一个标准的目录结构。Maven鼓励使用标准目录布局，这样就不需要进行额外 的配置，而且有助于各个不同工程之间的联接。当然，Maven也允许定制个性的目录布局，这就需要进行更多的配置。关于Maven的标准目录布局，请见参考资源[6]中的附录B.1。
4 Maven的优点
    [1]build逻辑可以被重用。在Ant中可能需要多次重复地写相同的语句，但由于POM的继承性，可以复用其它的POM文件中的语句。这样既可以写出清晰的build语句，又可以构造出层次关系良好的build工程。
    [2]不必关注build工作的实现细节。我们只需要使用一些build生命周期短语就可以达到我们的目标，而不必管Maven是如何做到这些的。如，只需要告诉Maven要安装(install)，那么它自然就会验证，编译，打包，及安装。
    [3]Maven会自动加载工程依赖的artifact所依赖的其它artifact(Transitive Dependency)，而不用显示的将这些artifact全部写到dependency中。
    [4]如果完全使用Maven的标准目录布局，那么可以极大地减少配置细节。
5 实例
5.1 构想
    由于只是阐述Maven的基本使用方法，所以本文将要设计的实例，只是一个简单的Maven demo。该实例包含两个工程：普通应用程序工程(app)和Web应用工程(webapp)。app工程提供一个简单的Java类；webapp工程只 包含一个Servlet，并将使用app中的Java类。
    该Demo的目标是能够正确地将webapp制成war包，以供部署时使用。要能够正确制作war，自然首先就必须要能够正确的编译源代码，且要将App模块制成jar包。本文创建的工程所在的目录是D:\maven\demo。
5.2 App工程
    可以使用Maven的archetype插件来创建新工程，命令如下：
    D:\maven\demo>mvn archetype:create -DgroupId=ce.demo.mvn -DartifactId=app
该工程的groupId是ce.demo.mvn，那么该工程的源文件将放在Java包ce.demo.mvn中。artifactId是app，那么该工程根目录的名称将为app。
    当第一次执行该命令时，Maven会从central仓库中下载一些文件。这些文件包含插件archetype，以及它所依赖的其它包。该命令执行完毕后，在目录D:\maven\demo下会出现如下目录布局：
app
|-- pom.xml
`-- src
    |-- main
    |   `-- java
    |       `-- ce
    |           `-- demo
    |               `-- mvn
    |                   `-- App.java
    `-- test
        `-- java
            `-- ce
                `-- demo
                    `-- mvn
                        `-- AppTest.java
因本文暂时不涉及JUnit测试，故请将目录app\src\test目录删除(不删除也没关系 ^_^)。然后再修改App.java文件，其完全内容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">package ce.demo.mvn;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">public class App screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    public String getStr(String str) screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        return str;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    }
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">}
其实，如果我们能够清楚地知道Maven的标准目录布局，就可以不使用archetype插件来创建工程原型；如果我们要定制个性的目录布局，那么就更没有必要使用archetype插件了。
5.3 WebApp工程
    我们仍然如创建app工程一样使用archetype插件来创建webapp工程，命令如下：
    D:\maven\demo>mvn archetype:create -DgroupId=ce.demo.mvn -DartifactId=webapp -DarchetypeArtifactId=maven-archetype-webapp
    第一次运行此命令时，也会从central仓库中下载一些与Web应用相关的artifact(如javax.servlet)。此命令与创建app的命 令的不同之处是，多设置了一个属性archetypeArtifacttId，该属性的值为maven-archetype-webapp。即告诉 Maven，将要创建的工程是一个Web应用工程。创建app工程时没有使用该属性值，是由于archetype默认创建的是应用程序工程。同样的，执行 完该命令之后，会出现如下标准目录布局：
webapp
|-- pom.xml
`-- src
    `-- main
        `-- webapp
            [size=+0]|-- index.jsp
            |-- WEB-INF
                `-- web.xml
    根据5.1节的构想，webapp工程将只包含一个Servlet，所以我们不需要index.jsp文件，请将其删除。此时大家可以发现，目前的目录布 局中并没有放Servlet，即Java源文件的地方。根据参考资源[6]中的附录B.1，以及app工程中Java源文件的布局，可以知道 Servlet（它仍然是一个Java类文件）仍然是放在webapp\src\main\java目录中，请新建该目录。此处的Servlet是一个简单HelloServlet，其完整代码如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">package hello;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import java.io.IOException;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import java.io.PrintWriter;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.ServletException;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServlet;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServletRequest;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import javax.servlet.http.HttpServletResponse;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">import ce.demo.mvn.App;  // 引用app工程中的App类
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">public class HelloServlet extends HttpServlet screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    private static final long serialVersionUID = -3696470690560528247L;
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    public void doGet(HttpServletRequest request, HttpServletResponse response)
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">            throws ServletException, IOException screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">{
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        App app = new App();
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        String str = app.getStr("CE Maven Demo");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        PrintWriter out = response.getWriter();
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("<html><body>");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("<h1>" + str);
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        out.print("</body></html>");
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    }
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">}
5.4 POM文件
    大家可以发现，在前面新建工程时，我们并没有提到各个工程中的pom.xml文件。现在将要讨论这个问题。我们先看看app工程中的POM文件，其完整内容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <artifactId>app</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <packaging>jar</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <name>CE Maven Demo -- App</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    大家可以发现此我帖出来的内容与实际由archetype插件生成的POM文件的内容有些不同，但基本上是一致的。只是为了使文件中的语句更清晰，此处删 除了一些冗余的内容，并修改了该工程的version和name的值，以与此例子的背景来符合。在目前情况下modelVersion值将被固定为 4.0.0，这也是Maven2唯一能够识别的model版本。groupId，artifactId的值与创建工程时使用的命令中的相关属性值是一致 的。packaging的值由工程的类型决定，如应用程序工程的packaging值为jar，Web应用工程的packaging值为war。上述情况 也可以从webapp的POM文件中看出，下面将看看这个pom的完整内容。
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <artifactId>webapp</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <packaging>war</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <name>CE Maven Demo -- WebApp</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  <dependencies>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">      <dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <groupId>ce.demo.mvn</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <artifactId>app</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">          <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">      </dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <groupId>javax.servlet</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <artifactId>servlet-api</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <version>2.4</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <scope>provided</scope>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    </dependency>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">  </dependencies>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    比较app与webapp中的POM，除前面已经提过的packaging的差别外，我们还可以发现webapp中的POM多了dependencies 项。由于webapp需要用到app工程中的类(见HelloServlet源代码)，它还需要javax.servlet包(因为该包并不默认存在于 jsdk中)。故，我们必须要将它们声明到依赖关系中。
5.5 执行
    上述两个工程创建完毕后，就需要执行一些命令来看看会有什么结果出现。我们首先进入app目录，并执行命令mvn compile，然后会在该目录下发现新生成的目录target\classes，即编译后的class文件(包括它的包目录)就放在了这里。再执行命令mvn package，在目录target中就会生成app-1.0.jar文件。该文件的全名由如下形式确定：artifactId-version.packaging。根据第2章的叙述可以知道，执行命令mvn package时，将首先将产生执行命令mvn compile之后的结果，故如果要打包，那么只需要执行mvn package即可。
    在app工程中执行完之后，就需要进入webapp工程了。进入webapp目录，此次将只执行mvn package命令(隐示地执行了compile过程)。此次命令的执行并不成功，会出现如下问题：
D:\maven\demo\webapp>mvn package
……
Downloading: http://repo1.maven.org/maven2/ce/demo/mvn/app/1.0/app-1.0.pom
[INFO] ------------------------------------------------------------------------
[ERROR] BUILD ERROR
[INFO] ------------------------------------------------------------------------
[INFO] Error building POM (may not be this project's POM).
Project ID: ce.demo.mvn:app
Reason: Error getting POM for 'ce.demo.mvn:app' from the repository: Error transferring file
  ce.demo.mvn:app:pom:1.0
from the specified remote repositories:
  central (http://repo1.maven.org/maven2)
……
    由粗体内容可知，Maven正试图从central仓库下载app工程的artifact，但central仓库肯定不会有这个artifact，其结果 只能是执行失败!由第1章artifact名词的解释可知，被依赖的artifact必须存在于仓库(远程或本地)中，但目前webapp所依赖的app 必不存在于仓库中，所以执行只能失败。
    解决这个问题有两种方法：[1]将app-1.0.jar安装到仓库中，使它成为一个artifact；[2]构建一个更高层次的工程，使app和webapp成为这个工程的子工程，然后从这个更高层次工程中执行命令。
    第一种方法比较简单（见），此处将详细讨论第2种方法(见5.6节)。
5.6 更高层次工程
    我们可以将app和webapp的上一级目录demo作为这两个工程的 一个 更高层次工程，即使用app和webapp成为这个工程的子工程。为了使demo目录成为一个demo工程，只需要在这个目录下添加一个pom.xml文件，该文件内容如下：
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"><project>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <modelVersion>4.0.0</modelVersion>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <groupId>ce.demo</groupId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <artifactId>mvn-demo</artifactId>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <packaging>pom</packaging>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <version>1.0</version>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <name>CE Maven Demo</name>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">   
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    <modules>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <module>app</module>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">        <module>webapp</module>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0">    </modules>
screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onmouseover="if(this.width>screen.width*0.7) {this.resized=true; this.width=screen.width*0.7; this.style.cursor='hand'; this.alt='Click here to open new window\nCTRL+Mouse wheel to zoom in/out';}" onclick="if(!this.resized) {return true;} else {window.open(this.src);}" onmousewheel="return imgzoom(this);" alt="" border="0"></project>
    与app和webapp中的POM相比，demo的POM使用了modules项，modules用于声明本工程的子工程，module中的值对应于子工程的artifact名。而且该POM的packaging类型必须为pom。
    有了demo工程后，我们只需要在demo目录下执行相关命令就可以了。通过如下命令即可验证：
    [1]mvn clean – 消除工程(包括所有子工程)中产生的所有输出。这本文的实例中，实际上是删除target目录。由于之前的操作只有app工程产生了target目录，而webapp并没有，所以将只会删除app工程中的target目录。
    [2]mvn package – 将工程制作成相应的包，app工程是作成jar包(app-1.0.jar)，webapp工程是作成war包(webapp-1.0.war)。打开 webapp-1.0.war包，可以发现app-1.0.jar被放到了WEB-INF的lib目录中。
6 小结
    通过以上的叙述与实例，应该可以对Maven有一个粗略的认识了。使用Maven关键是要弄清楚如何写pom.xml文件，就如同使用Ant要会写 build.xml文件一样。在POM中可以直接写入Ant的task脚本，也可以调用Ant的build.xml文件(推荐)，所以Maven也可以完 成Ant的绝大多数工作(但不必安装Ant)。注意：使用Maven就不要再过多的使用Ant脚本。
    利用好Maven的继承特性及子工程的关系，可以很好地简化POM文件，并能够构建层次结构良好的工程，有利于工程的维护。
7 参考资源
[1]Maven官方网站. http://maven.apache.org
[2]Maven POM文件参考结构. http://maven.apache.org/ref/current/maven-model/maven.html
[3]Super POM. http://maven.apache.org/guides/introduction/introduction-to-the-pom.html
[4]Maven主要插件的列表. http://maven.apache.org/plugins
[5]Maven基本使用指南. http://maven.apache.org/guides/index.html
[6]Better Build with Maven. http://www.mergere.com/m2book_download.jsp -- 强烈推荐
[7]介绍Maven2. http://www.javaworld.com/javaworld/jw-12-2005 /jw-1205-maven_p.html
[8]揭秘Maven2 POM. http://www.javaworld.com/javaworld/jw-05-2006/jw-0529-maven.html
[9]Maven让事情变得简单. http://www-128.ibm.com/developerworks/cn/java/j-maven
[10]Maven文档集. http://docs.codehaus.org/display/MAVENUSER/Home
[11]有效利用Maven2的站点生成功能. http://www.matrix.org.cn/resource/article/44/44491_Maven2.html
http://www.blogjava.net/jiangshachina/admin/EditPosts.aspx中的第一个主题